Nuclear factor kappa B (NF-κB) belongs to a family of closely related homo- and hetero-dimeric transcription factor complexes composed of various combinations of the Rel/NF-κB family of polypeptides. NF-κB and related family members are involved in the regulation of more than 50 genes relating to immune and inflammatory responses ((Barnes P J, Karin M (1997) N Engl J Med 336, 1066-1071) and (Baeuerle P A, Baichwal V R (1997) Adv Immunol 65, 111-137)). In most cell types, NF-κB is present as a heterodimer comprising a 50 kDa and a 65 kDa subunit (p50/RelA). The heterodimer is sequestered in the cytoplasm in association with inhibitor of NF-κB (IκB)family of proteins to be kept in an inactive state. IκB-family proteins mask the nuclear translocation signal of NF-κB. Upon stimulation of cells with various cytokines (e.g. TNF-α, IL-1), CD40 ligand, lipopolysaccharide (LPS), oxidants, mitogens (e.g. phorbol ester), viruses or many others. IκB proteins are phosphorylated at specific serine residues, poly-ubiquitinated, and then degraded through a proteasome-dependent pathway. Freed from IκB, the active NF-κB is able to translocate to the nucleus where it binds in a selective manner to preferred gene-specific enhancer sequences. Among the genes being regulated by NF-κB are many coding for pro-inflammatory mediators, cytokines, cell adhesion molecules, and acute phase proteins. Expression of several of these cytokines and mediators in turn can lead to further activation of NF-κB via autocrine and paracrine mechanisms.
Broad evidence is available that suggests a central role of NF-κB in many inflammatory disorders including airway inflammation and asthma ((Yang L et al., J Exp Med 188 (1998), 1739-1750), (Hart L A et al. Am J Respir Crit Care Med 158 (1998), 1585-1592), (Stacey M A et al., Biochem Biophys Res Commun 236 (1997), 522-526) (Barnes P and Adcock I M, Trends Pharmacol Sci 18 (1997), 46-50)).
Further, it has been shown that glucocorticoids, which are by far the most effective treatment for asthma, inhibit airway inflammation by directly interacting with and inhibiting the activity of the transcription factors NF-κB and activating peptide-1 (AP-1) ((Barnes P (1997) Pulmon Pharmacol Therapeut 10, 3-19) and (Dumont A et al. (1998) Trends Biochem Sci 23, 233-235)).
In general, inhibition of NF-κB activation results in strong anti-inflammatory effects similar or superior to those brought upon by steroids. Consequently, NF-B inhibition should improve inflammatory symptoms typical for asthma; allergic rhinitis; atopic dermatitis; hives; conjunctivitis; vernal catarrh; rheumatoid arthritis; systemic lupus erythematosus; psoriasis; diabrotic colitis; systemic inflammatory response syndrome; sepsis; polymyositis; dermatomyositis; Polyaritis nodoa; mixed connective tissue disease; Sjoegren's syndrome; gout, and the like.
Further, several studies imply that NF-κB plays an essential role in neoplastic transformation. For example, NF-κB is associated with cell transformation in vitro and in vivo as a result of gene overexpression, amplification, rearrangement, or translocation (Mercurio, F., and Manning, A. M. (1999) Oncogene, 18:6163-6171). In certain human lymphoid tumor cells, the genes of NF-κB family members are rearranged or amplified. Its possible involvement in cancer pathology is also disclosed in Mayo, M. W., Baldwin A. S. (2000) Biochmica et Biophysica Acta 1470 M55-M62. Mayo M. W. et al., discloses the inhibition of NF-κB results in the blockage the initiation and/or progression of certain cancer, particularly colorectal cancer.
Finally, NF-κB may also be involved in the regulation of neuronal cell death. It has been shown that NF-κB becomes activated and promotes cell death in focal cerebral ischemia (Nature medicine Vol. 5 No. 5, May 1999).
Extensive research during the past years led to the identification of an IκB kinase (IKK) complex as being responsible for the signal-induced IκB phosphorylation ((Mercurio, F., and Manning, A. M. (1999) Current Opinion in Cell Biology, 11:226-232), (Mercurio, F., and Manning, A. M. (1999) Oncogene, 18:6163-6171), (Barnkett, M., and Gilmore T. D. (1999) Oncogene 18, 6910-6924), (Zandi, E., and Karin, M., (1999) 19:4547-4551), (Israel, A., (2000) trends in CELL BIOLOGY 10:129-133), and (Hatada, E. N, et al. (2000) Current Opinion in Immunology, 12:52-58)). This complex is most likely the site of integration of all of the different stimuli leading to NF-κB activation. The IKK-complex (molecular weight 700-900 kDa) is composed of various proteins including two homologous IκB kinases, called IKK-α and IKK-β, an upstream kinase, NIK which induces NF-κB, a scaffold protein called IKAP, which tethers together the three kinases, and a regulatory subunit IKK-γ, which preferentially interacts with IKK-β.
IKK-β is a 756 amino acid serine-threonine kinase showing 52% identity to and the same domain structure as IKK-α ((Mercurio F et al. (1997) Science 278, 860-866.), (Woronicz J D et al. (1997) Science 278, 866-869.), (Zandi E et al. (1997) Cell 91, 243-252.). IKK-β forms homo-dimers and hetero-dimers with IKK-α in vitro and in cells, respectively. IKK-β also interacts with IKK-γ, IKAP, NIK and IκBα. Recombinant IKK-β phosphorylates IκBα and IκBβ at specific serine residues with equal efficacy (Li J et al. (1998) J Biol Chem 273, 30736-30741.), (Zandi E, Chen Y, Karin M (1998) Science 281, 1360-1363.). IKK-β shows a higher constitutive kinase activity as compared to IKK-α. This is in agreement with data suggesting that over-expression of IKK-β activates the transcription of a NF-κB-dependent reporter gene with a higher efficacy as compared to IKK-α. IKK-β has been shown to be activated in various cell lines or fresh human cells in response to various stimuli including TNF-α, IL-1β, LPS, anti-CD3/anti-CD28 co-stimulation, protein kinase C and calcineurin, B-cell receptor/CD40 ligand stimulation, and vanadate. IKK-β is activated in fibroblast-like synoviocytes (FLS) isolated from the synovium of patients suffering from rheumatoid arthritis or osteoarthritis (Zandi E et al. (1997) Cell 91, 243-252.), (O'Connell M A et al. (1998) J Biol Chem 273, 30410-30414.), (Kempiak S J et al. (1999) J Immunol 162, 3176-3187.). Furthermore, IKK-β can be activated by the structurally related upstream kinases MEKK-1 and NIK, most likely through phosphorylation of specific serine residues within the T-loop (activation loop) and by certain protein kinase C isoforms ((Nakano H et al. (1998) Proc Natl Acad Sci USA 95, 3537-3542.), (Lee F S et al. (1998) Proc Natl Acad Sci USA 95, 9319-9324.), (Nemoto S et al., (1998) Mol Cell Biol 18, 7336-7343.), (Lallena M J et al. (1999) Mol Cell Biol 19, 2180-2188.)). A catalytically inactive mutant of IKK-β has been shown to inhibit activation of NF-κB by TNF-α, IL-1β, LPS, anti-CD3/anti-CD28 stimulation ((Mercurio F et al. (1997) Science 278, 860-866.), (Woronicz J D et al (1997) Science 278, 866-869.)). The same effects are observed when MEKK1 or NIK are overexpressed. Additionally, IKK-β mutations in the activation loop inhibited IL-1 and TNF-α signaling (Delhase M et al. (1999) Science 284, 309-313.). Based on the experimental results described above, there is clear-cut evidence for a pivotal involvement of IKK-β in various pathways leading to NF-κB activation.
In summary, the specific inhibition of IKK-β should result in a strong anti-inflammatory and immuno-modulatory effect in vivo with the potential of improving the underlying causes of asthma and other diseases. In addition, anti-tumor and anti-ischemic effects of an IKK-β inhibitor may be expected.
Manna et al., disclose 4,6-disubstituted 3-cyano-2-aminopyridines represented by general formulas: wherein (R′, R″) represent (OCH3, OCH3), (Cl, Cl), (H, Cl), (H, Br), (H, CH3), (H, OCH3), (H, NO2), or (H, N(CH3)2),or as a general anti-inflammatory, analgesic, and antipyretic agent (Eur J. Med. Chem. 34, 245-254(1999)).
Manna et al. neither disclose pyridine derivatives with aliphatic groups at position 4 of the pyridine ring, nor suggest IKK-β kinase or NF-κB inhibitory activity on the above known pyridine derivatives.
The development of a novel compound having effective anti-inflammatory actions based on a specific and selective inhibitory activity to NF-κB has been desired.